Benign prostatic hyperplasia (BPH) is a common disorder in middle-aged and older men, with prevalence increasing with age. At age 70, more than one-half of men have symptomatic BPH, and nearly 90% of men have microscopic evidence of an enlarged prostate. The severity of symptoms also increase with age with 27% of patients in the 60-70 age bracket having moderate-to-severe symptoms, and 37% of patients in their 70's suffering from moderate-to-severe symptoms.
The prostate early in life is the size and shape of a walnut and weighs about 20 grams. Prostate enlargement appears to be a normal process. With age, the prostate gradually increases in size to twice or more its normal size. The fibromuscular tissue of the outer prostatic capsule restricts expansion after the gland reaches a certain size. Because of such restriction on expansion, the intracapsular tissue will compress against and constrict the prostatic urethra thus causing resistance to urine flow.
FIG. 1 is a sectional schematic view the male urogenital anatomy, with the walnut-sized prostate gland 100 located below the bladder 105 and bladder neck indicated at 106. The walls 108 of bladder 105 can expand and contract to cause urine flow through the urethra 110, which extends from the bladder 105, through the prostate 100 and penis 112. The portion of urethra 110 that is surrounded by the prostate gland 100 is referred to as the prostatic urethra 120. The prostate 100 also surrounds the ejaculatory ducts 122 which have an open termination in the prostatic urethra 120. During sexual arousal, sperm is transported from the testes 124 by the ductus deferens 126 to the prostate 100 which provides fluids that combine with sperm to form semen during ejaculation. On each side of the prostate, the ductus deferens 126 and seminal vesicles 128 join to form a single tube called an ejaculatory duct 122. Thus, each ejaculatory duct 122 carries the seminal vesicle secretions and sperm into the prostatic urethra 120.
Referring to FIGS. 2A-2C, the prostate glandular structure can be classified into three zones: the peripheral zone, transition zone, and central zone. The peripheral zone PZ, which is the region forming the postero-inferior aspect of the gland, contains 70% of the prostate glandular elements in a normal prostate (FIGS. 2A-2C). A majority of prostate cancers (up to 80%) arise in the peripheral zone PZ. The central zone CZ surrounds the ejaculatory ducts 122 and contains about 20-25% of the prostate volume. The central zone is often the site of inflammatory processes. The transition zone TZ is the site in which benign prostatic hyperplasia develops, and contains about 5-10% of the volume of glandular elements in a normal prostate (FIG. 2C), but can constitute up to 80% of such volume in cases of BPH. The transition zone TZ consists of two lateral prostate lobes and the periurethral gland region indicated at 130. As can be understood from FIGS. 2A-2C, there are natural barriers around the transition zone TZ, i.e., the prostatic urethra 120, the anterior fibromuscular stroma FS, and a fibrous plane FP between the transition zone TZ and peripheral zone PZ. In FIGS. 2A-2C, the anterior fibromuscular stroma FS or fibromuscular zone can be seen and is predominantly fibromuscular tissue.
BPH is typically diagnosed when the patient seeks medical treatment complaining of bothersome urinary difficulties. The predominant symptoms of BPH are an increase in frequency and urgency of urination. BPH can also cause urinary retention in the bladder which in turn can lead to lower urinary tract infection (LUTI). In many cases, the LUTI then can ascend into the kidneys and cause chronic pyelonephritis, and can eventually lead to renal insufficiency. BPH also may lead to sexual dysfunction related to sleep disturbance or psychological anxiety caused by severe urinary difficulties. Thus, BPH can significantly alter the quality of life with aging of the male population.
BPH is the result of an imbalance between the continuous production and natural death (apoptosis) of the glandular cells of the prostate. The overproduction of such cells leads to increased prostate size, most significantly in the transitional zone which traverses the prostatic urethra.
In early stage cases of BPH, treatments can alleviate the symptoms. For example, alpha-blockers treat BPH by relaxing smooth muscle tissue found in the prostate and the bladder neck, which may allow urine to flow out of the bladder more easily. Such drugs can prove effective until the glandular elements cause overwhelming cell growth in the prostate.
More advanced stages of BPH, however, can only be treated by surgical interventions. A number of methods have been developed using electrosurgical or mechanical extraction of tissue, and thermal ablation or cryoablation of intracapsular prostatic tissue. In many cases, such interventions provide only transient relief, and there often is significant peri-operative discomfort and morbidity.
In a prior art thermal ablation method, RF energy is delivered to prostate tissue as schematically depicted in FIGS. 3A-3B. FIG. 3A depicts the elongated prior art RF needle being penetrated into a plurality of locations in a prostate lobe. In a first aspect of the prior art method, the elongated RF needle typically is about 20 mm in length, together with an insulator that penetrates into the lobe. The resulting RF treatment thus ablates tissue away from the prostatic urethra 120 and does not target tissue close to, and parallel to, the prostatic urethra 120. In another aspect of the prior art RF method, the application of RF energy typically extends for 1 to 3 minutes or longer which allows thermal diffusion of the ablation to reach the capsule periphery. Such prior art RF energy delivery methods may not create a durable effect, since smooth muscle tissue and alpha adrenergic receptors are not uniformly ablated around the prostatic urethra. As a result, tissue in the lobes can continue to grow and impinge on the urethra thus limiting long term effectiveness of the treatment.